1. Field of the Invention
The present invention relates to a decompression apparatus and an inorganic porous body used therein. More particularly, the invention relates to a decompression apparatus having an exhaust mechanism which incorporates a cylindrical inorganic porous body therein and an inorganic porous body used therein.
2. Related Art
In conventional manufacturing processes of a semiconductor wafer or a liquid crystal material, a vacuum chamber which is used as part of a dry etching apparatus, a sputtering apparatus, a CVD apparatus, a heat treatment furnace, or the like has a slow exhaust passage parallel to a main exhaust passage for buffering the pressure at the time of exhausting under various conditions such as a low pressure or a gas atmosphere having a different composition than air.
As shown in FIG. 8, a conventional decompression apparatus 31 has an exhaust mechanism 33 for decompressing a vacuum chamber 32. The exhaust mechanism 33 has a main exhaust passage 37. One end of the main exhaust passage 37 is located in the vacuum chamber 32 and is connected to an exhaust opening 35 to which a plate-like alumina filter is attached. The other end of the main exhaust passage 37 is connected to a vacuum pump 36. The exhaust mechanism 33 further has a first opening/closing valve (main valve) 38 which is disposed in the main exhaust passage 37, a slow exhaust passage 39 one end of which is connected to the vacuum chamber 32 directly or via the main exhaust passage 37 and other end of which is connected to the vacuum pump 36 via the main exhaust passage 37, and a second opening/closing valve (slow exhaust valve) 40 which is disposed in the slow exhaust passage 39 and is made parallel to the first opening/closing valve 38.
In the conventional decompression apparatus 31, exhausting is performed slowly through the slow exhaust passage 39 at an initial stage and then very fast through the main exhaust passage 37.
However, when exhausting through the plate-like alumina filter 34, because the pore diameters of a porous body (the alumina filter) is small, the exhausting rate is extremely low.
FIG. 9 shows another conventional decompression apparatus 41. In this decompression apparatus, a slow exhaust opening 42 equipped with a plate-like alumina filter 34 is provided separately from an exhaust opening 35 for increasing the exhaust rate. However, modifying the apparatus in this manner requires high cost.
On the other hand, a method using a metallic mesh filter instead of the plate-like alumina filter provides such advantages that an influence on the exhaust time is small due to a large mesh size and that the filter can be attached to the exhaust opening in the apparatus without modifying the apparatus. However, such the method shows a small effect of suppressing stirring-up of particles.
Further, there have been proposed a wafer handling system which has a main exhaust passage that communicates with a vacuum chamber and a vacuum pump and a slow exhaust passage that is parallel to the main exhaust passage (refer to Japanese Unexamined Patent Publication JP-A-61-228648, for example) and a horizontal processing furnace having a variable conductance valve disposed in a slow exhaust passage (refer to Japanese Unexamined Patent Publication JP-A-7-235497, for example).